Galaxies that speed through the intergalactic medium will have their gas and material stripped away, but on a year-by-year basis, the changes are imperceptible. Image credit: NASA, ESA Acknowledgements: Ming Sun (UAH), and Serge Meunier.

“We are not the same persons this year as last; nor are those we love. It is a happy chance if we, changing, continue to love a changed person.” -W. Somerset Maugham

After 13.8 billion years have gone by, you might not think that a year makes much of a difference. A year to the Universe is like 0.2 seconds — the literal blink of an eye — to a human being. Yet even though changes might be gradual, they’re real, and they very much add up over time.

A region of the Orion Nebula, one of the largest and most rapidly-star-forming regions where star birth takes place. Image credit: NASA, ESA and the Hubble Heritage Team.

The Earth’s rotation slows, the Moon moves farther away, the Sun heats up, the Big Bang’s leftover glow cools down, stars are born, the galaxies recede and so much more. If we look closely and precisely enough, we can even measure exactly how — and by how much — these changes occur.

A deep field of distant galaxies, which are all receding from us and getting ever-closer to unreachable. Some of them have already crossed that threshold. Image credit: NASA, ESA, the GOODS Team and M. Giavalisco (STScI).

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Ethan. So if a SN did go off in our galaxy, even if behind thick dust, could we miss it? Clearly we wouldn’t see it in visible light, but IR, radio, X-ray, and even neutrinos might be capable of announcing its occurrence. So is there much of a chance we could still miss it?